- Jul 19, 2017 -
All metals react with oxygen in the atmosphere, forming an oxide film on the surface. Unfortunately, the formation of iron oxides on ordinary carbon steel continues to oxidize, causing corrosion to continue to expand, eventually forming holes. You can use paint or oxidation-resistant metals (e.g., zinc, nickel, and chromium) to insure the surface of the carbon steel, but, as people know, this protection is only a thin film. If the protective layer is damaged, the steel below begins to rust.
The corrosion resistance of stainless steel depends on chromium, but because chromium is one of the components of steel, the protection methods are different.
When the amount of chromium added to more than 11.7%, the atmospheric corrosion resistance of steel increased significantly, but the chromium content is higher, although the corrosion resistance can still be improved, but not obvious. The reason is that when the steel is alloyed with chromium, the type of surface oxide is changed into a surface oxide similar to that formed on the pure chromium metal. This tightly bonded rich chromium oxide protects the surface and prevents further oxidation. This oxide layer is extremely thin, through which it can see the natural luster of the steel surface, so that stainless steel has a unique surface. Moreover, if the surface is damaged, the exposed surface of the steel will be repaired with the atmospheric reaction, and the oxide "passivation film" can be formed again, and the protective effect will continue.